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jorge1
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Join Date: Jul 2013
Posts: 15

Demagnetization of Permanent Magnets

10/10/2013 5:09 AM

Dear colleagues,

I have the values for a magnet used in a permanent magnet generator and it is stated that maximum temperature is 140ºC, which I believe is the Curie temperature. Also it is stated that minimum Br is 1.40T. So, these are the values for the intrinsic curve, isnt it?

The temperature at rated load is calculated at 75ºC and Br is 1.20T.

As far as I have seen in all the normal curves, as far as you increase the temperature you decrease the value of remanent flux density. So, according that... shouldnt Br(1.20T) for 75ºC be higher than Br(1.40T) from 140ºC?

I am pretty sure that I am making a mess... but dont find why...

Thank you very much for your help,

Best regards,

Jorge
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Pathfinder Tags: Demagnetization permanent magnets
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mjb1962853
Guru
Engineering Fields - Electrical Engineering - Analog and Digital Circuit Design Engineering Fields - Electromechanical Engineering - Transformers, Motors & Drives, EM Launchers Engineering Fields - Engineering Physics - Applied Electrical, Optical, and Mechanical

Join Date: Jan 2008
Location: NY
Posts: 1207
Good Answers: 119
#1

Re: Demagnetization of permanent magnets

10/10/2013 8:18 AM

Curie temperature (>310C for NdFeB) is usually much higher than maximum operating temperature. Specification of 140C should be below point where "small" (but permanent) demagnetization occurs. Minimum Br=1.4T is probably at 20C. Br=1.2T at 75C seems reasonable. I think you may be misinterpreting the supplied specs. Try this link...

http://www.magmamagnets.com/permanent-magnet-stability
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jorge1
Active Contributor

Join Date: Jul 2013
Posts: 15
#3
In reply to #1

Re: Demagnetization of permanent magnets

10/10/2013 4:19 PM

Thanks for your answer!

So probably 140ºC is not Curie... but they are specifying it as if it wasnt...

Ok, you are confirming what I was thinking about. It cant be 1.4T for 140ºC.

Thank you very much!!! :)


Regards,

Jorge
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HUX
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Join Date: Jan 2007
Location: UK S.Northants
Posts: 485
Good Answers: 19
#2

Re: Demagnetization of Permanent Magnets

10/10/2013 10:43 AM

I forgot all about this. I use neodymiums to hold flying leads in place, they are araldited to the copper contacts. When resoldering a wire to the contact I demagnetized the magnet. Next time I will used double-sided tape so the magnet can be removed prior to any soldering work and reattached later.
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jorge1
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Join Date: Jul 2013
Posts: 15
#4
In reply to #2

Re: Demagnetization of Permanent Magnets

10/11/2013 2:20 AM

Thanks for your answer :)
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